Cake Board Masonite Square, 20 x 20 x 1/4 Inches by GSACake Board Masonite Square, 20 x 20 x 1/4 Inches by GSA. Masonite is a high density engineered wood fiberboard. Large cakes placed on Masonite cake boards will not sag in the middle when you pick them up. This prevents sagging and wrinkle marks in your icing and decorations. Wrap them in color foil- when you need to use them again just re-wrap with new foil. Most decorators charge a deposit and write their name on the back side of the board to insure their return. They can also be used to separate tiered cakes.